1. Field of Invention
The present invention relates to light sources and concentrators, specifically to light sources that provide concentrated light of various colors, especially for optical scanning systems. Such optical scanning systems include, but are not limited to xerographic devices, line scan imaging systems, and area scan imaging systems. Common embodiments of these scanners include computer-input and flat-bed page scanners, such as the model HP9195A manufactured by Hewlett Packard Company of Palo Alto, Calif. U.S.A. and sold under the trademark "Scan Jet Plus".
2. Description of Prior Art
It is desirable to obtain the highest possible concentration of light, for instance, in illumination systems of optical scanners in order to maximize the dynamic range of such devices.
Prior art illuminators are shown in U.S. Pat. Nos. 4,013,915 to W. H. Duft (1977), 4,225,042 to J. D. Armitage (1981), 4,963,933 to Kenneth Brownlee (1990), and 5,001,609 to Robert Gardner et al. (1991). These illuminators are of the types depicted in FIGS. 1 and 2.
The illuminator shown in FIG. 1 uses a light source 10, which comprises several individual sources positioned at the base of a reflector 12. Reflector 12 has reflecting walls 14 which diverge outwardly. The cross section of this prior-art illuminator has a salient geometric shape such as conical (not shown), or it may extend any length perpendicular to its cross section. A diffuser 16 is located at the diverging end of reflector 12. As light is emitted by source 10, it will spread out. Some will proceed directly to diffuser 16, spreading out slightly as indicated, and some will be reflected from walls 14, as also indicated. As a result, most of the light emitted by source 10 will shine through diffuser 16 and the surface of diffuser 16 will appear to be uniformly illuminated.
However, the illumination intensity at the surface of diffuser 16 is much less than that of source 10 since light is dispersed from the relatively small surface of source 10 to cover the much larger area of diffuser 16.
FIG. 2 shows a modification of the illuminator of FIG. 1. In this case, reflecting walls 14' are parallel to each other, so that the light source and the diffuser areas are equal. Here, the light intensity at the surface of the diffuser, here designated 16', is somewhat greater than the light intensity at the surface of diffuser 16 of FIG. 1, but is still less than the intensity of the light source.
The main drawback of the above devices is their inability to concentrate radiation emitted by the light source. Moreover, to use these illuminators in a color scanning device, where different colors must be emitted at different times, one must employ mechanically operated color filters (not shown), which would add complexity to the apparatus. Furthermore, since the switching from one color to the next is done mechanically, the speed of the scanning process decreases.
Non-patent literature also discusses the subject of nonimaging light concentrators. As stated in the article "Nonimaging Optics" by R. Winston (Scientific American, March 1991), nonimaging concentrators intensify light flux much better than do lenses. According to the article, an optical device that concentrates light by forming an image will blur that image away from the focal point. Consequently, a maximum concentration of light can be attained only when the image-forming requirements are disregarded. In his experiments, Winston uses a solar energy concentrator, which is essentially a funnel. Light entering the large side of the funnel is reflected from the walls of the funnel so that most of it passes out through the small side of the funnel, thus destroying any imaging order (image) present in the light source. However, if only concentration of light is desired, there is no need for image formation.
The article also describes a solar concentrator having hyperbolic walls. Such a device is useful when light must be concentrated on a flat surface. While this device is able to concentrate light, it lacks any capability for use in color copiers or scanners, where concentrated light of various colors must be supplied at respectively different times.